X-ray diffraction contrast tomography (dct) system, and x-ray diffraction contrast tomography (dct) method

ABSTRACT

An X-ray diffraction contrast tomography system (DCT) comprising a laboratory X-ray source ( 2 ), a staging device ( 5 ) rotating a polycrystalline material sample in the direct path of the X-ray beam, a first X-ray detector ( 6 ) detecting the direct X-ray beam being transmitted through the crystalline material sample, a second X-ray detector ( 7 ) positioned between the staging device and the first X-ray detector for detecting diffracted X-ray beams, and a processing device ( 15 ) for analysing detected values. The crystallographic grain orientation of the individual grain in the polycrystalline sample is determined based on the two-dimensional position of extinction spots and the associated angular position of the sample for a set of extinction spots pertaining to the individual grain.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of application Ser. No. 12/913,034,filed Oct. 27, 2010 which claims the benefit of priority from DanishPatent Application No. PA 2010 70324 filed on Jul. 9, 2010, all of whichare incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO A MICROFICHE APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION

The present invention relates to an X-ray diffraction contrasttomography (DCT) system comprising an X-ray source for providing anX-ray beam in a direct path; a staging device for positioning androtating a polycrystalline material sample in the direct path of theX-ray beam; a first X-ray detector located in the direct path with thestaging device positioned between the first X-ray detector and the X-raysource, allowing said first X-ray detector to detect a direct X-ray beambeing transmitted through the crystalline material sample; and aprocessing device for analysing detected values and determiningcrystallographic grain centre-of-mass positions and grain orientationsin the polycrystalline material sample.

Such a DCT system is described in the article “X-ray diffractioncontrast tomography: a novel technique for three-dimensional grainmapping of polycrystals. Part 1: direct beam case” published in Journalof Applied Crystallography (2008), 41, 319-326. A synchrotron X-ray beamis used to illuminate the sample, and the X-ray detector detects acombined absorption contrast and diffraction contrast image of thetransmitted beam. By subtracting the absorption contrast part, it ispossible from the remaining diffraction contrast to perform tomographyof grains embedded in a polycrystalline mono-phase material. Withtraditional absorption or phase contrast tomography only the outercontour of a mono-phase specimen could be detected. With X-raydiffraction contrast tomography, the grains of the polycrystallinematerial sample under examination are imaged using the occasionallyoccurring diffraction contribution to the X-ray attenuation coefficientin the non-diffracted X-ray beam leaving the crystalline materialsample. Each time a grain fulfils the Bragg diffraction condition adiffraction contrast occurs. The diffraction contrast appears on thedetector behind the sample as an extinction spot caused by a localreduction of the transmitted beam intensity recorded on the detector. Inthe article, the three-dimensional grain shapes are reconstructed from alimited number of projections using algebraic reconstruction techniques(ART). The procedure for the three-dimensional grain shapereconstruction is based on spatial filtering criteria only, and theprocedure can therefore be performed without analysing the grainorientations. With respect to grain orientations the article specifiesthat the intensity of the diffractions spots must be included in orderto determine orientations, and even with integrated intensities severalsolutions may exist and choices have to be made. It is explained in thearticle that overlapping diffraction contrasts present a problem andthat the sample consequently had to have only little grain orientationspread, grains of approximately the same size and tailored transversesample dimensions in order to limit the probability of spot overlap.

Considerable efforts have been put into the development of techniquesfor three-dimensional grain mapping of polycrystalline materials. Thesetechniques are utilizing X-ray beams from a synchrotron facility andemploy reconstruction algorithms of the kind known in tomography inorder to provide a non-destructive characterization of a sample ofpolycrystalline material.

Conventional X-ray absorption tomography systems as disclosed in U.S.Pat. No. 5,245,648 are able to provide a spatial representation of asample of crystalline material. However, the contrast of such spatialrepresentation is based on the densities of the sample and if the samplehas a homogeneous density, it therefore only represents the periphery ofthe sample. Furthermore, if the sample comprises several phases ofdifferent materials, the internal structure within each of these phasesis not visible in the representation. Moreover, the densities do notprovide information of the grain structure of a crystalline materialsample and hence no information about the orientation (or stress) of thegrain lattice, which is equally important to determine as the spatialrepresentation of the sample.

BRIEF SUMMARY OF THE INVENTION

The present invention aims at improving X-ray diffraction contrasttomography by making it easier to obtain the grain mapping, also from alarger sample of a mono- or multi-phase polycrystalline material.

With a view to this the X-ray diffraction contrast tomography systemaccording to the present invention is characterized in that a secondX-ray detector is positioned between the staging device and the firstX-ray detector for detecting diffracted X-ray beams leaving thecrystalline material sample at an angle, said second X-ray detectorbeing adapted to allow at least a fraction of the direct X-ray beamleaving the polycrystalline material sample to continue to the firstX-ray detector, and that the X-ray source is a laboratory X-ray source.

The second X-ray detector detects the diffracted X-ray beams andprovides information on the crystalline structure in the grain causingthe diffraction. The diffracted beam exits from the sample in an anglethat is larger when the spacing between the planes in the crystallattice is smaller. In prior art X-ray diffraction contrast tomographymeasurements for mapping of polycrystals, the X-ray source is asynchrotron X-ray source like the ID19 beamline of the EuropeanSynchrotron Radiation Facility in Grenoble, France. Synchrotron X-raysources are very large facilities that are located in only a limitednumber of places in the world. By dispensing with such synchrotron X-raysources and instead making the X-ray source a laboratory X-ray sourcethe equipment used for X-ray diffraction contrast tomography becomesavailable for more common use, and it requires much less space. By usinga laboratory X-ray source the diffraction contrast tomography becomesaccessible to material science institutes in both universities and inthe private sector. A laboratory X-ray source has rather small outerdimensions, such as a maximum size of less than 10 metres, and in orderto enhance a compact set up the second X-ray detector detectingdiffracted X-ray beams is positioned between the staging device and thefirst X-ray detector, and all or at least a fraction of the direct beamis allowed to pass the second X-ray detector.

In an embodiment an X-ray magnifier device is positioned in the directpath of the X-ray beam between the staging device and the first X-raydetector. The magnifier device enlarges the beam image on the firstdetector and allows a more detailed detection of the two-dimensionalextent and position of the individual extinction spot, and thus a moreprecise grain shape reconstruction of the grain microstructure in thesample. The enlarged beam image also provides more detail in theabsorption or phase contrast tomography information, such as presence ofcracks or inclusions in the grain structure.

In a further development of this embodiment, the magnifier devicemagnifies the cross-sectional area of the beam onto the first X-raydetector to be at least 10 times larger than the cross-sectional area ofthe beam impinging on the sample. The 10 times magnification increasesthe resolution of the image by a factor 10 without changing the firstdetector. As an alternative, the resolution of the first detector couldbe increased but that typically involves more costs, and in some casesit is impossible, as there are intrinsic limitations on the spatialresolution of all existing x-ray detectors. It is preferred that themagnifier device magnifies the cross-sectional area of the beam onto thefirst X-ray detector to be at least 80 times larger than thecross-sectional area of the input beam. With a first detector having aresolution of e.g. 4 micrometer and a magnification of 80 times theresulting resolution on positions in the sample is 50 nm. Crystallinematerials such as metals and ceramics that may be analysed by theabove-mentioned techniques are important in processes of manufacturingfor instance Solid Oxide Fuel Cells (SOFC) and micro-electronics. Thesematerials typically have grain sizes in the range of 0.5-2 micrometerand it is highly desirable to have a non-destructive and generallyavailable characterization, allowing the internal micro structuralfeatures such as triple-phase boundaries in SOFCs and micro-cracks to becorrelated to the grains structure and associated crystallographicinformation of a sample of crystalline material.

In an embodiment the magnifier device is a Fresnel zone-plate or acompound refractive lens located in the direct path between the seconddetector and the first detector. Although it is possible to locate themagnifier device between the staging device and the first detector, thepreferred location between the second detector and the first detectorprovides the advantage that diffracted beams are completely undisturbedby the presence of the magnifier device and the second detector can bearranged at a distance from the staging device which is optimum fordetection of the diffracted beams.

Preferably the first detector is positioned less than 5 metres indistance from the X-ray source as this would allow setting up theequipment in most ordinary buildings. For table top embodiments of theX-ray DCT system it is preferred that the first detector is positionedless than 2 metres in distance from the X-ray source. One advantage of asmall distance is that the X-ray beam may travel through air at ambientpressure, and thus it may be possible to dispense with the traditionalevacuation of the enclosure around the X-ray beam.

In an embodiment of the X-ray diffraction contrast tomography system abeam conditioning X-ray optics device is positioned in the direct pathbetween the X-ray source and the staging device. The X-ray optics devicemay e.g. monochromatise the X-ray beam in order to make the X-ray beammore suitable for use in diffraction measurements where the diffractionangle depends upon the wavelength of the X-ray beam.

In an embodiment the staging device is adapted to rotate thepolycrystalline material sample while the sample is exposed to the X-raybeam. The staging device can make exposures for a set of nominalrotation angles, where for each exposure the stage rotates through apredetermined angular interval around the nominal rotation angle.Alternatively, the rotation angle may remain fixed at the nominal valuefor each exposure.

In a situation being theoretically ideal, the second detector ispositioned and sized so that it detects all of the diffracted X-raybeams, which are sufficiently intense to be above the signal-to-noiselimit of the set-up. However, the X-ray diffraction contrast tomographysystem is capable of performing the grain mapping and reconstructionsolely based on the X-ray extinction spot detected on the firstdetector, in particular when the sample has small dimensions inhorizontal section so that grains that simultaneously cause diffractiononly to a small extent overlap in the direct path of the beam. However,for larger samples having a large number of grains, such as more than500 grains or more than 1100 grains, overlapping diffracting grains maypose problems for the reconstruction. The diffraction spots detected onthe second detector can then be used to sort out which of the extinctionspots detected on the first detector pertain to a particular grain. Asevery grain causes many extinction spots during 180° or 360° rotation ofthe sample it is not necessary to detect all the correspondingdiffraction spots in order to perform useful sorting of the extinctionspots. In an embodiment where the second X-ray detector extend along atleast 40% of the area through which the diffracted X-ray beams pass, itis possible to perform such useful sorting, and the second X-raydetector may thus be located only to one side of the direct path of theX-ray beam, such as above but not below the beam. Due to symmetries inthe crystal lattice structure a full set of information may be acquiredwhen the second X-ray detector extend along at least 60% of the areathrough which the diffracted X-ray beams pass.

In an embodiment said second X-ray detector is adapted to allow thedirect X-ray beam leaving the polycrystalline material sample tocontinue to the first X-ray detector by having a central hole or acentral slit providing free passage of the X-ray beam in the directpath. In this manner the second X-ray detector may surround the directpath through all 360° and yet allow the X-ray beam to pass on to thefirst X-ray detector. It is an advantage to be able to detect on fullDebye-Scherrer rings as misalignments of the staging device in relationto the direct path may then be compensated for when the detected valuesare analysed.

In an embodiment the second X-ray detector positioned closest to thestaging device has a spatial resolution which is at least 5 times lessprecise than the spatial resolution of the first X-ray detector. Thelower resolution of the detector positioned closest to the stagingdevice brings the advantage of lower cost of this detector.

The present invention also relates to an X-ray diffraction contrasttomography method of determining a multi-dimensional representation ofgrain structures in a polycrystalline material sample, where an X-raysource provides an X-ray beam in a direct path; a staging devicepositions and rotates the polycrystalline material sample in the directpath of the X-ray beam; and a first X-ray detector located in the directpath detects a direct X-ray beam leaving the crystalline materialsample, and a processing device analyses values received from the X-raydetector and identifies X-ray extinction spots by a reduced intensity ofthe detected beam, when a spot occurs, and records for each determinedX-ray extinction spot the two-dimensional position of the extinctionspot and the angular position of the polycrystalline sample. The valuesanalysed in the processing device are typically images received from theX-ray detector.

In the previously mentioned article: Journal of Applied Crystallography”(2008), 41, 319-326, the grain mapping comprises two steps: sortingextinction spots according to grain of origin (known as indexing) andconstruction of the 3D grain morphologies (using ART). The sorting ofthe grains is based on using the intensity distributions of theextinction spots in order to determine grain orientations. Theintensities of the diffraction spots are difficult to detect with thedesired accuracy, and as already mentioned the present invention aims atimproving X-ray diffraction contrast tomography by making it easier toobtain the grain mapping.

With this in view and according to the present invention, the processingdevice determines the crystallographic grain orientation and thecentre-of-mass position of the individual grain in the polycrystallinematerial sample based on said two-dimensional position and said angularposition for a set of extinction spots pertaining to the individualgrain. By avoiding use of the intensity distribution of the extinctionspots to determine the grain orientations it is no longer necessary todetermine the precise values of intensities of the spots but fullysufficient to just determine the actual presence of extinction spots.This is in particular an advantage in case the direct beam is magnifiedbefore it forms the images on the first X-ray detector, because themagnification weakens the intensity of the beam and thus also weakensdifferences in intensities.

In a further development of the method the processing device analysesvalues received from a second X-ray detector detecting diffracted X-raybeams leaving the polycrystalline material sample at an angle, and basedon the values received from the second X-ray detector the processingdevice determines at least one of the following characteristics: a) thecrystal structure (position of atoms in the unit cell) of one or moreindividual crystalline phases present in the sample, and b) strain ingrains in the polycrystalline material sample. In this modified methodit is thus possible to obtain more detailed information on eitherinformation detected on the first X-ray detector for contrast tomographypurposes or information detected on the first X-ray detector fordiffraction purposes.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

Illustrative examples of the invention will now be explained below withreference to the very schematic drawings, in which

FIG. 1 illustrates an X-ray diffraction contrast tomography systemaccording to the present invention,

FIG. 2 illustrates a sample and a first X-ray detector and a secondX-ray detector according to the invention, and

FIGS. 3 a-3 d illustrations of a second X-ray detector detail allowingpassage of at least a fraction of the direct X-ray beam.

DETAILED DESCRIPTION OF THE INVENTION

In the context of the present invention a laboratory X-ray source meansa compact X-ray source. The laboratory X-ray source has much smallerouter dimensions than traditional synchrotron X-ray sources, saidsynchrotron sources having typical diameters in the range from 30 to1000 metres, whereas laboratory X-ray sources have typically a maximumouter dimension of 10 metres or less. Laboratory X-ray sources may be ofthe type having an X-ray tube, in which electrons are accelerated in avacuum by an electric field and shot into a target piece of metal.X-rays are emitted as the electrons decelerate in the metal. The outputspectrum has a continuous spectrum of X-rays with sharp peaks inintensity at certain energies depending on the kind of metal used forthe target, such as copper, tungsten, silver, rhodium or molybdenum.Laboratory X-ray sources may also be of a laser type or of anotheravailable type having maximum outer dimensions of 10 metres or less,such as less than 5 metres. Laboratory X-ray sources are available fromsuppliers, such as Lyncean Technologies, Inc., Palo Alto, Calif., USA;Xradia Inc., Concord, Calif., USA; Proto Manufacturing Ltd., Ontario,Canada; SkyScan, Kontich, Belgium, and Phoenix X-ray, Wunstorf, Germany.

FIG. 1 depicts an X-ray diffraction contrast tomography system 1. Thesystem 1 comprises a laboratory X-ray source 2 emitting a beam of X-raysin a direct path 3. The X-ray beam passes through a beam conditioningX-ray optics device 4 which may condition the beam as required. The typeof conditioning depends on the X-ray source used, and as an example theconditioning can monochromatise the beam if it has a spread inwavelengths or the conditioning may involve condenser optics, whichserves to capture a larger portion of the radiation emitted from theX-ray source 2, and focussing it on the sample. Such condensing istypically useful when the X-ray source is of the type with an X-raytube. However, the use of a beam conditioning X-ray optics device 4 maybe superfluous and be dispensed with if the X-ray beam radiated by theX-ray source is sufficiently focussed and sufficiently monochrome.

A staging device 5 is adapted to position and rotate a crystallinematerial sample 10 in the direct path 3 of the X-ray beam. Such astaging device is very well-known in X-ray diffraction techniques, andit comprises a material sample or specimen holder and a stage foradjusting and rotating the material sample. The stage may be motorisedand may also be translated transversely out of the direct path 3 of thebeam in order to acquire reference images of the beam profile. The stagehas a central, rotational axis Z and the position of the stage can beadjusted so that this rotational axis Z is perpendicular to the directpath 3 of the X-ray beam. The stage can rotate the material sample 10about rotational axis Z either with a predefined, settable rotationalspeed such as in the range from 20 minutes to 5 hours per full rotationof 360° or in stepwise, incremental rotational movements that may besettable such as in the range from 0.01° to 15° per incrementalrotation. For every nominal rotation angle where exposure is to occur,the stage may additionally rotate or oscillate about rotational axis Zthrough a predetermined angular interval around the nominal rotationangle. The stage has a default reference point for the rotationalposition of 0°, and preferably also a possibility for setting an actualreference point at initiation of the rotational movement of a mountedmaterial sample. The current rotational angle ω of the stage withrespect to the reference point is communicated from the staging device 5to a processing device 15. As an example, a staging device and sampleholder may be obtained from the firm Bruker AXS GmbH, Karlsruhe,Germany.

A first X-ray detector 6 is positioned in the direct path 3 of the X-raybeam. This first detector 6 has a two-dimensional detector screencapable of detecting X-rays. The screen orientation is preferably sothat the surface of the two-dimensional flat screen of the firstdetector is about perpendicular to the direct path 3. In the embodimentillustrated in FIG. 1 an X-ray magnifier device 8 is located between thestaging device 5 and the first X-ray detector 6 so that the image on thescreen of the detector is enlarged in comparison to the cross-sectionalarea of the X-ray beam leaving the material sample 10. In the embodimentof FIG. 2 there is no such magnifier device, and the X-ray beam leavingthe material sample 10 thus arrives unmagnified to the first detector 6.As one example out of many possible, the first detector 6 may be acamera with a detector of the type charge-coupled device (CCD) or afluorescent screen coupled to a CDD. One specific example of such afirst X-ray detector is the taper optics CCD fast-readout low-noisedetector developed by the European Synchrotron Radiation Facility(ESRF), cf. Journal of Synchrotron Radiation, (2006), 13, 260-270.

A second X-ray detector 7 is positioned between the material sample inthe staging device 5 and the first X-ray detector and it has a centralportion 12 in which the X-ray beam in the direct path 3 may passunhindered through the second detector 7 and onwards to the first X-raydetector 6. The central portion 12 may be a through-going hole in thesecond detector 7 or it may be a hole or bore that reduces the thicknessof the material in the second detector 7 to such an extent that theremaining material does not significantly attenuate the beam leaving thematerial sample 10. FIG. 3 a depicts a partial view of the seconddetector 7 in the area surrounding a slit 112 passing through thematerial of the second detector. The slit is located in the path of thedirect beam and provides free passage of the direct X-ray beam leavingthe material sample so that the entire beam leaving the sample continuesto the first X-ray detector 6. FIG. 3 b depicts a partial view of thesecond detector 7 in the area surrounding a hole or aperture 113 passingthrough the material of the second detector. The aperture 113 is locatedin the path of the direct beam and provides free passage of the directX-ray beam leaving the material sample so that the entire beam leavingthe sample continues to the first X-ray detector 6. FIG. 3 c depicts apartial view of the second detector 7 in the area surrounding an area ofreduced thickness 114 in the material of the second detector. The areaof reduced thickness is located in the path of the direct beam andprovides passage of a fraction of the direct X-ray beam leaving thematerial sample so that said fraction of the beam leaving the samplecontinues to the first X-ray detector 6. The reduced thickness ispreferably so thin that said fraction of the beam is at least 10%, suchas in the range from 20% to 99%, and preferably at least 60%. FIG. 3 dillustrates a second detector 7 made up of two parts 7 a, 7 b located ata distance from one another about the path of the direct X-ray beamleaving the material sample so that a free passage 115 exists betweenthe two parts 7 a, 7 b through which there is free passage of the directX-ray beam leaving the material sample.

The orientation of the second X-ray detector 7 is preferably so that thesurface of the two-dimensional flat screen of the detector is aboutperpendicular to the direct path 3. In an alternative embodiment thesecond X-ray detector is a screen panel located only to one side of thedirect path 3, and in a further embodiment the second X-ray detector isan arch-shaped flat screen positioned to one side of the direct beam andextending partly onto the other side of the direct beam 3, like ahalf-moon covering more than 180° of the circumference around the directbeam. In a further alternative embodiment the second X-ray detector iscomposed of two halves located at such a distance from one another thatthe direct beam 3 can pass unhindered in the space between the twohalves.

The second X-ray detector may be of the same type as the first X-raydetector, but preferably it is of a type having less spatial resolutionand larger field-of-view than the first detector. The resolution of thefirst X-ray detector may be in the range of 2 to 20 micro-metres, whenit is of the charge-coupled device (CCD) type, or it may be of higher orlower resolution according to the desired detail of the material samplesto be analysed. The resolution of the second X-ray detector 7 may bemuch less precise, such as from 50 to 200 micrometers. This allows for amore simple system, and the lower requirement for resolution of thesecond detector is possible because the second detector mainly has todetect the scattering angle of the diffraction, whereas the first X-raydetector has to determine the actual position and extent of theextinction spots with high accuracy.

The polycrystalline material sample 10 is illustrated in FIG. 2. Whenthe staging device 5 rotates the material sample 10, or position thesame in different rotational positions, and the sample is exposed to theX-ray beam in the direct path 3 then a diffraction occurs every time thelattice in a grain is oriented so with respect to the incoming beam inthe direct path 3 that the Bragg diffraction condition is fulfilled.

The Bragg diffraction equation states that 2dsinθ=nλ, where d is theinterplanar distance between lattice planes in the grain, n is aninteger, λ is the wavelength of the X-ray, and θ is the scatteringangle. When the beam from the X-ray source impinges the crystallinematerial sample positioned by the staging device 5 one or more grain ofthe crystalline material sample may fulfil the diffraction conditionsdetermined by Bragg's law resulting in diffraction 9 of the X-raysimpinging the grains and fulfilling the diffraction conditions.

When diffraction occurs in a crystal grain 11 a part of the intensity ofX-ray beam in the direct beam 3 is scattered (directed) in anotherdirection, namely in direction of a line 9 forming the angle 2θ with thedirect beam 3. Due to the diffraction some of the intensity of thedirect beam 3′ in the area covered by the grain has been removed fromthe direct beam 3, and consequently an extinction spot 13 of lessintensity can be detected on the first X-ray detector 6, and theposition and the extension of the extinction spot in the two-dimensionalarea of the first detector 6 can be recorded. Due to the fact that thefirst X-ray detector 6 is in the line of the direct beam 3 it isconsequently possible to detect the two-dimensional position of thegrain in the sample 10 in this manner, but not the position in thedirection of the direct beam 3. The scattered portion of the beamfollows the line 9 and is detected on the second X-ray detector 7 as anilluminated diffraction spot 14.

The processing device 15 receives information in form of values for thedetection of an extinction spot and the two-dimensional position of theextinction spot 13, and it associates this information with theinformation received from the staging device 5 on the correspondingrotational angle ω of the staging device.

Each grain is associated with a lattice, which will have numerouslattice planes that give rise to diffraction when the material sample isrotated through 90°, and for symmetry reasons even more diffractionswhen rotated through 180° or 360°, by the staging device 5. The numberof visible diffraction events caused by a single grain may be in therange from 20 to 100. The intensity of the diffraction spots andextinction spots will vary, and it is much more demanding to detect theprecise intensity than the sole fact that diffraction actually occurred.

Based on the detected information a grain reconstruction has to beperformed both with respect to the three-dimensional geometricalposition and extension of the individual grains and with respect to theorientation of the lattice in the individual grain. In order to do sothe processing device 15 analyses the detected values and performs asorting of the detected spots into subsets that may pertain to the samegrain. One possible manner of doing this is to sort the extinction spots13 into groups having nearly identical vertical limits (upper and lowerlimits), as the vertical position of a grain remains constant while thematerial sample is rotated. Such a sorting will however not discernbetween grains positioned in an overlapping manner along the direct path3, while producing simultaneous diffractions.

In the following there is described examples of a method of how to solvethis and provide reconstructed grains orientations based on extinctionspots, also in a large material sample having hundreds of grains orthousands of grains, even when the grains have large varieties in grainsorientations and grain sizes.

The reconstruction of the crystalline material sample should beapplicable both in case an X-ray diffraction contrast tomography systemis deployed with only the first X-ray detector 6 detecting only theextinction spots 13 resulting from grains fulfilling the diffractioncondition, and in the situation where an X-ray diffraction contrasttomography system is deployed with both the first X-ray detector 6detecting extinction spots 13 and with the second X-ray detector 7detecting X-ray diffraction spots 14. Although the method according tothe present invention is made for the latter system with two X-raydetectors 6, 7 it is also applicable to the former system having only asingle detector 6.

The first and second X-ray detector 6, 7 communicate with the processingdevice 15, such as a standard computer connected to the system 1.Besides from receiving signals representing the detected extinctionspots 13 and diffraction spots 14, the processing device preferably alsocontrols the staging device 5 so that the crystalline material sample isautomatically rotated in a programmed manner during the exposureprocess. Preferably the processing device 15 also controls x-rayshutter(s) (not shown) required to determine the timing of the exposuresof the two detectors. The shutter or shutters are placed along the beampath. The shutter is a heavily absorbing piece that may be moved in andout in front of the detector to determine when and for how longexposures are made. The one or more shutters can be placed in the beampath before or after the sample or both before and after the sample. TheDCT system typically also comprises a housing or enclosure (not shown).The housing may be arranged with a possibility for evacuation of airfrom the area surrounding the beam path.

Due to difficulties in precisely determining the decrease in intensityof an extinction spot 13 or the intensity of a diffraction spot 14, theintensity is left out of the X-ray diffraction contrast tomographymethod. During one 180° rotation of the material sample there willtypically be recorded many thousands of extinction spot events. For eachevent the geometric centre of area position of the extinction spot isdetermined and recorded in form of the two dimensions y, z, where y andz are the planar coordinates of the centre of area position. The centreof area position coincides in the plane with the crystallographic graincentre-of-mass position. For each event the rotational position w of thematerial sample is also recorded.

In a six-dimensional space where the three dimensions are the usualthree-dimensional geometric space, typically denoted x, y and z, and theremaining three dimensions represent the lattice plane orientation of agrain, typically denoted by the Miller indices (hkl) for the planeorthogonal to the vector direction h, k, l. For each extinction spot theposition dimensions y, z and the rotational position w are recorded. Thedirection of the direct path 3 in relation to the sample 10 is alsoknown for the specific rotational position ω, so the position dimensionsy, z are located on a one-dimensional line in the six-dimensional space.The extinction spot occurs at the rotational angle co and the extinctionspot represents a two-dimensional lattice plane in the grain. In thesix-dimensional space the coordinates for the line and the coordinatesfor the plane are known for the grain. The grain producing theextinction spot is consequently located on a three-dimensional plane inthe six-dimensional space.

Each individual of the many thousands of recorded extinction spot eventsis positioned on a three-dimensional plane in the six-dimensional space.The extinction spots pertaining to the same individual grain share themutual condition that all the three-dimensional planes intersect in apoint in the six-dimensional space. The coordinates for this point arethe three-dimensional position in the geometrical space and theorientation of the lattice in the grain. Several different standardmathematical procedures exist for calculating the intersection pointsfor three-dimensional planes in a six-dimensional space. By calculatingthe intersection points the extinction spots are separated in setspertaining to individual grains, and this is done without usinginformation on the intensity of the individual extinction spot. Themethod is consequently robust and easy to apply and avoids use of theintensity of the spots. The method also provides the advantage that thecrystallographic grain orientation of the individual grain is obtaineddirectly by the determination of the intersection points.

In another example of a method of how to reconstruct grain orientationsbased on the two-dimensional position of the extinction spots detectedon the first detector 6 and the corresponding angular position ω of thematerial sample, there is firstly established a theoretical model ofprofiles and then the measured profiles are compared and paired with thetheoretical profiles.

In order to establish a theoretical model the material sample isdiscretized into voxels having smaller volume than the average grainsize of the material sample. The size of the voxels may be chosen sothat in average at least ten or more voxels pertain to one and the samephysical grain in the material sample. The theoretical model is then foreach voxel discretized with respect to the orientation space, and foreach possible orientation a theoretical profile is established. Theindividual profile includes information of the occurrence of extinctionspots as a function of the angular positions ω of the material sample.There is consequently for each theoretical grain orientation in thecrystalline material sample determined a theoretical profile comprisinginformation of the extinction spots 13 as a function of the angularposition co of the staging device 5.

The profile data of the theoretical model are stored by the processingdevice 15 in a lookup table. The extinction spots 13 detected on thefirst X-ray detector 6 are ordered into profiles according to thegeometrical location in the two-dimensional plane of the detector,corresponding to the two-dimensional position of voxels in the materialsample, as a function of the angular positions ω of the material sample.The detected profiles are compared with the theoretical profiles in thelookup table and paired with the closest matching theoretical profiles.In this manner the orientation of each grain of the crystalline materialsample is determined without considering the intensities of theextinction spots. The crystallographic grain orientation and thecentre-of-mass position of the individual grain in the polycrystallinematerial sample are determined based solely on said two-dimensionalposition and said angular position ω for the set of extinction spotspertaining to the individual grain.

In yet another method the processing device 15 utilises values detectedon the second X-ray detector 7 and representing diffraction spots 14.The diffraction spots 14 are located on Debye-Scherrer rings, the radiusof which depends on d, the interplanar distance between lattice planesin the grain. The radial position of the diffraction spot as well as theactual two-dimensional position on the second detector 7 may firstly beutilised to associate particular diffraction events to certain grains,and secondly be utilised to qualify the lattice characteristics of theindividual grain. For given materials there are a limited number ofspecific lattice forms, and the interplanar distance d between latticeplanes can be used to identify the crystalline phases present in thegrain, and it can further be used to identify strain in the grains,because strain in the grain changes the distance d. The additionalinformation retrieved by using the data from the second detector may beapplied to any of the above-mentioned methods.

Details from the above-mentioned embodiments and examples may becombined into other embodiments and examples within the scope of thepatent claims.

1. An X-ray diffraction contrast tomography method of determining amulti-dimensional representation of grain structures in apolycrystalline material sample having grains, where an X-ray sourceprovides an X-ray beam in a direct path, a staging device positions androtates the polycrystalline material sample in the direct path of theX-ray beam, an X-ray detector detects diffraction spots from diffractedX-ray beams leaving the crystalline material sample, a processing deviceanalyses values received from the X-ray detector and representingdiffraction spots; wherein the processing device based on the valuesreceived from said X-ray detector determines at least one of thefollowing characteristics: a) the crystal structure of one or moreindividual crystalline phases present in the sample, and b) strain ingrains in the polycrystalline material sample, and wherein said X-raysource is a laboratory X-ray source having a target piece of metal,which X-ray source provides a continuous output spectrum of X-rays withsharp peaks in intensity at certain energies depending on the metal ofthe target piece.
 2. An X-ray diffraction contrast tomography methodaccording to claim 1, wherein an X-ray detector located in the directpath detects a direct X-ray beam leaving the crystalline materialsample.
 3. An X-ray diffraction contrast tomography method according toclaim 2, wherein the processing device analyses values received from theX-ray detector located in the direct path and identifies X-rayextinction spots by a reduced intensity of the detected beam, when aspot occurs, and records for each determined X-ray extinction spot thetwo-dimensional position of the extinction spot and the angular positionof the polycrystalline sample, wherein the processing device determinesthe crystallographic grain orientation and the position of theindividual grain in the polycrystalline material sample based on saidtwo-dimensional position and said angular position for a set ofextinction spots pertaining to the individual grain.
 4. An X-raydiffraction contrast tomography method according to claim 1, wherein thestaging device rotates the polycrystalline material sample in stepwise,incremental rotational movements.
 5. An X-ray diffraction contrasttomography method according to claim 4, wherein the stepwise,incremental rotational movements are settable.